It looked at games with lots of expansions but not really clear information about which were the best ones. Thanks to everyone who voted for sharing your knowledge and experience. This geeklist shows the results to date for those polls. The polls are all still open so if you don't agree with the results you can still vote in them.

Base Game is incomplete without it / Essential / Fixes the base game Would always/often want to include this / Great / Adds a lot Adds a little / Okay / Nice to have A waste of money / Poor / Inconsequential Actively harmful / Bad / Breaks the game

For each game I calculate a Necessity Rating for each expansion by awarding points: 3/2/1/0/-1 for the five ratings above and then converting this to a score out of 10. A '10' rating would be "Essential", '7' is "Great", '3' is "Okay", Zero is "A waste of money" and "Actively Harmful" would be a negative.

The polls geeklist didn't include the expansions where it seems common knowledge which expansions are essential to get the best out of a base game, but it did include links to some geeklists that had done just that. But for completeness here are a few of the biggies:

Not many answers for this one and an explanation of why it was hard to rate the expansions from TedW: "Each additional deck gives you an increasing number of combinations to fight. So, while you don't need all the decks having some of them is definitely worthwhile.Once you have all (most of) the decks, the Emissaries are a great add and again extend the life of the game. However, one emissary w/out the other is not a good buy nor are the emissaries without the other races."

Bonus cards and Rough Roads Ahead cards are part of the Big Expansion, and the Compatibility Pack doesn't do anything except replace components with identically-functioning ones that look different (so that the expansion works with the old edition).